Method for controlling an electric motor driving a body in translation

ABSTRACT

The invention concerns a method for controlling an electric motor driving a body in translation between an initial position and a final position determined by a stop, by powering the motor with reduced voltage in the final position approach phase. The motor has a torque/speed characteristic such that the torque at null speed decreases with the supply voltage. As the approach phase starts, the method consists in determining a reduced voltage by decreasing the rotational speed of the motor from a nominal value to a predetermined reduced value and in cutting the motor power supply if the motor rotational speed drops below a predetermined threshold value.

[0001] The subject of the invention is a method of controlling anelectric motor driving a body in translation between an initial positionand a final position determined by an abutment, according to which themotor is supplied at reduced voltage in the phase of approach to thefinal position.

[0002] The subject of the invention is also a device for theimplementation of this method.

[0003] The invention relates more particularly to devices for shadingand for solar protection such as doors and venetian blinds, arm-mountedblinds, etc.

[0004] Such a method and such devices are known from the patent FR 2 717016 in the name of the applicant. This patent teaches the instigating ofa particular supply phase for the motor, in particular the reducing ofthe voltage, in the phase of approach to the final position determinedby an abutment. This particular supply phase is obtained by means of anelectric circuit which reduces the torque of the motor. The motor usedis an asynchronous motor with capacitor whose operating curve isrepresented as a reminder in FIG. 1 of the appended drawing, in whichthe torque C is represented along the ordinate and the speed N isrepresented along the abscissa. FIG. 1 represents two curves for twodifferent supply voltages, that is to say two different abutmenttorques. These curves have a common point, the no-load speed, that is tosay for a torque equal to zero. It is noted that a decrease in theabutment torque also entails a decrease in the torque available to drivethe load. This method and the device for its implementation are suitablefor installations in which the resisting torque due to the load reducesby itself before the instigation of the particular supply phase. Such isthe case with windup shutters where the influence of the weight of theshutter decreases as it is wound up and for arm-mounted blinds where theeffort required drops steeply once the arms have unlocked and for whichthe torque, at this instant, is generally small and hardly influenced atall by the weight of the fabric. In this case, it is possible to use oneand the same circuit for rolling shutters or arm-mounted blinds ofdifferent weights. For certain installations, the fact that it is notpossible to reduce the abutment torque without reducing the torqueavailable in the approach phase, constitutes a considerable drawback.Such is the case with installations where the resisting torque remainssubstantially constant throughout the movement of the moving body, forexample installations of the venetian blind type. In this case, thecharacteristics of the motor must be chosen in such a way that thetorque under load is similar to the abutment torque. This requires amatching of the operating characteristic of the motor, that is to say ofthe control circuit, or even of the motor itself, to each weight of bodydriven.

[0005] The objective of the invention is to remedy this drawback, thatis to say to obtain automatic matching of the operating characteristicof the motor to the load.

[0006] The method according to the invention is characterized in that amotor is used whose torque/speed characteristic is such that thezero-speed torque decreases with the supply voltage, in that at thestart of the approach phase a reduced voltage is determined bydecreasing the speed of rotation of the motor from a nominal value to apredetermined reduced value and the supply to the motor is cut if thespeed of rotation of the motor falls below a predetermined thresholdvalue.

[0007] Motors exhibiting such a characteristic are very well-knownmotors, such as separately excited DC motors, brushless motors anduniversal motors. With, as sole reference, the speed, a matching of theabutment force to the load is thus obtained without any expedient.

[0008] The control of the speed of a motor driving a venetian type blindis certainly known, for example from the patent U.S. Pat. No. 5,170,108.This control is however performed only so as to maintain the speed ofmovement of the blind within a certain span and to halt the motor whenthe speed falls below a minimum, this drop being interpreted as anobstacle or an abutment.

[0009] According to a first mode of implementation of the method, toreduce supply voltage corresponding to the predetermined reduced speedis maintained throughout the approach phase. Hence, one merely reducesthe voltage once.

[0010] According to a second mode of implementation of the method,during the phase of approach to the final position, the motor issupplied at reduced voltage while controlling the speed in such a way asto maintain it at the predetermined value. In this way, in the approachphase, the torque is continuously tailored to the residual load and theabutment torque is correspondingly reduced.

[0011] According to another mode of implementation of the method, duringthe phase preceding the phase of approach to the final position, themotor is supplied at a voltage such that the speed of the motor is equalto a predetermined speed. In this way, the speed of movement of the bodyis substantially identical from one installation to another, regardlessof its weight.

[0012] The subject of the invention is also a device for theimplementation of the method characterized in that it comprises meansfor measuring the speed of the motor, an LPU (logic processing unit) andan LPU-motor power interface.

[0013] According to one mode of execution of the device, the means formeasuring the speed of the motor consist of a sensor delivering pulsesand the LPU comprises means for calculating the position and the speedof the motor, a memory in which is permanently recorded theinstantaneous position of the motor, speed and threshold presets and apreset for entry into the phase of approach to the final position, aprogram for comparing the position and the measured speed with presetsand means for generating a power interface control signal.

[0014] According to one mode of execution, the power interface consistsof a chopped supply and the LPU comprises a pulse generator andpulse-width modulation means, the modulated pulses being applied to thechopped supply.

[0015] According to another mode of execution, the power interfaceconsists of a stabilized and frequency-regulated supply and the controlsignal generated by the LPU is a signal of variable frequency.

[0016] The method according to the invention and its means ofimplementation will be described in greater detail in conjunction withthe appended drawing in which:

[0017]FIG. 2 diagrammatically represents the torque/speed characteristicof the motor used in the method according to the invention, for varioussupply voltages of the motor;

[0018]FIG. 3 is a chart similar to that of FIG. 2 comprising valuesillustrating the method according to the invention;

[0019]FIG. 4 is a block diagram of a device for the implementation ofthe method in its application to the driving of a venetian blind;

[0020]FIG. 5 represents the flowchart of the program of the LPUaccording to a first mode of execution of the method and

[0021]FIG. 6 represents the flowchart of the LPU according to a secondmode of execution of the method.

[0022] In the chart represented in FIG. 2, the straight line adiagrammatically represents the shape of the torque/speedcharacteristic, that is to say of the relation between the torque andthe speed for a specified supply voltage. This characteristic is veryapproximately a straight line. The characteristic shifts parallel toitself when the supply voltage varies. The curves b, c and d correspondto three different supply voltages, the supply voltage decreasing fromcurve a to curve d.

[0023] In the initial phase, the motor is supplied at the nominalvoltage Un. The corresponding characteristic of the motor is representedby the curve a in FIG. 3.

[0024] In the particular supply phase, that is to say the phase ofapproach to the final position, the supply voltage of the motor isdecreased until the speed of the motor is equal to a predetermined valueV2, for example 30 rpm. As may be seen in FIG. 3, the operatingcharacteristic of the motor at the speed V2, that is to say its supplyvoltage, varies with the load. For a load of 0.8 Nm we are located oncurve c. The abutment torque, that is to say the torque at zero speed,is substantially equal to 1 Nm.

[0025] If, for example, the load is equal to 0.5 Nm, one is then locatedon curve c and the torque at the abutment is substantially equal to 0.7Nm. Thus, by adjusting the speed by means of the voltage and without anyother expedient, the torque at the abutment is automatically tailored tothe load.

[0026]FIG. 4 diagrammatically represents the application of theinvention to the driving of a blind S of venetian blind type, that is tosay comprising a bottom rail BR and slats SL which stack up in theraised position of the blind. This blind is driven by a motor M suppliedby way of a power interface PI controlled by a logic processing unitLPU. With the motor is associated a position sensor PS for example aHall effect sensor linked to the spindle of the motor and deliveringpulses making it possible to ascertain both the position of the spindleof the motor, that is to say the position of the shaft for winding upthe belts BT of the blind and the speed of the motor. The pulsesdelivered by the sensor are processed by the LPU which calculates theposition of the motor and its speed of rotation. The LPU comprises amemory in which the instantaneous position of the motor is continuouslyrecorded. In a learning phase, the memory also records speed presets V1,V2 and threshold presets as well as the preset for the position of entryinto the particular supply phase. The LPU is programmed to compare thespeed calculated at part of the pulses delivered by the sensor with oneor other of the speed presets V1, V2 and threshold preset and to delivera PWM (pulse width modulated) signal to the power interface PI whichconstitutes a chopped supply. The LPU is also programmed to compare theposition calculated from the pulses delivered by the sensor with theposition preset recorded in memory.

[0027] PWM generators are described in detail in the publication“INTELLIGENT MOTION PROCEEDING” of June 1993, pages 230 to 236, as wellas in the works “DESIGNERS' GUIDE TO POWER PRODUCTS” Application Manual,2^(nd) edition June 1992 by SGS-THOMSON microelectronics, pages 309 to322, the publication “POWER SEMICONDUCTOR APPLICATIONS” by PHILIPS,pages 3-4 to 3-10 and the SIEMENS publication “3-Phase Sine WaveGeneration with the SAB 80C515A and SAB 80C17A” by NikolaosPapadopoulos, Siemens Semiconductor Division, Rev. 2.0-e, March 1992.

[0028] PWM-based motor control. is moreover described in the patent U.S.Pat. No. 4,706,180.

[0029] The installation is controlled by a breaker IR, the closing ofwhich is interpreted by the LPU as an order to move.

[0030] Represented diagrammatically alongside the unwound blind is theinitial phase of movement A and the final phase B, that is to say thephase of approach to the docking position.

[0031] The installation represented in FIG. 4 can be embodied in anotherway. For example, the power interface could consist of a stabilizedsupply, for example frequency-regulated. In this case, the LPU woulddeliver a signal of variable frequency to the stabilized supply.

[0032] In its basic programming, the LPU is programmed according to thebasic logic diagram represented in the bottom half of the logic diagramof FIG. 5.

[0033] On entering the approach phase designated in FIG. 5 by the finalphase, the LPU delivers a PWM signal suitable for generating a voltagesuch that the motor rotates at the speed V2 and delivers a PWM signalsuitable for generating a voltage U. This voltage is maintainedthroughout the approach phase. The LPU continues to test the speed. Aslong as this speed is greater than the threshold S, the voltage U ismaintained. When the speed goes below the predetermined threshold, theLPU ceases to deliver the PWM signal and the supply to the motor is cut.The dropping of the speed below the threshold S signifies that thebottom rail of the blind has arrived at the abutment.

[0034] A first improvement of the method is represented by the upperpart of the logic diagram in FIG. 5. According to this improvement, inthe initial phase, the motor is supplied at a voltage such that thespeed of the motor has a predetermined value V1. In this way, the speedof movement of the blind is substantially identical from oneinstallation to another regardless of its weight. In the case of severalblinds operating simultaneously on one and the same facade of abuilding, a coordinated and hence more harmonious overall motion of theblinds is obtained.

[0035] In FIG. 3, the curves b and d represent characteristic curvescorresponding to a motor supply voltage such that the speed V1 is equalto 30 rpm for the loads of 0.8 Nm (b) and 0.5 Nm (d).

[0036] A second improvement is represented in FIG. 6 which represents amodification of the basic program.

[0037] As in the basic program, on entering the final phase, the LPUdelivers a PWM signal suitable for generating a voltage such that themotor rotates at the speed V2, then reads the corresponding voltage Uand delivers a PW signal suitable for generating this voltage U. Next,in contradistinction to the basic program, this voltage U is notmaintained throughout the final phase, rather the LPU continuously testswhether the speed V2 is maintained. If the speed increases, the LPUreduces the supply voltage U until the speed V2 is regained. In thismanner, the torque is continuously tailored to the residual load and theabutment torque is correspondingly reduced. Moreover, by avoiding anincrease in speed in the final phase, the aesthetics of the motion ofthe blind are enhanced. An increase in the speed of the blind may resultfrom a decrease in the load due, for example, to the effect of themoving weight or to the disappearance of friction or else to a momentaryoverload present at the time of the initialization of the particularsupply phase.

[0038] The method according to the invention is applicable to any bodymoving in translation and whose weight hardly varies during themovement. Such is also the case with rigid doors and counterweightdoors. The movement may be horizontal or vertical. In the case of arigid curtain moving vertically, the method is also applicable for thehalting of the curtain at the bottom point.

[0039] The preferred application of the method does not exclude itsapplication in the case of weight variation. In this case, the advantageof a reduced abutment force is also present.

1. A method of controlling an electric motor driving a body intranslation between an initial position and a final position determinedby an abutment, according to which the motor is supplied at reducedvoltage in the phase of approach to the final position, characterized inthat a motor is used whose torque/speed characteristic is such that thezero-speed torque decreases with the supply voltage, in that at thestart of the approach phase a reduced voltage is determined bydecreasing the speed of rotation of the motor from a nominal value to apredetermined reduced value and the supply to the motor is cut if thespeed of rotation of the motor falls below a predetermined thresholdvalue.
 2. The method as claimed in claim 1, characterized in that saiddetermined reduced voltage is maintained during the approach phase. 3.The method as claimed in claim 1 or 2, characterized in that thevariation in the speed of rotation of the motor is monitored during theapproach phase and in that, if the speed of rotation increases withrespect to its predetermined reduced value, the supply voltage of themotor is reduced so as to bring the speed of rotation of the motor downto its predetermined reduced value.
 4. The method as claimed in one ofthe preceding claims, characterized in that a nominal supply voltage ofthe motor is determined in a phase preceding the approach phase bybringing the speed of the motor to a predetermined nominal speed and inthat this nominal voltage determined using the phase preceding theapproach phase is maintained.
 5. A device for implementing the method asclaimed in one of claims 1 to 4, characterized in that it comprisesmeans for measuring the speed of the motor (PS), a logic processing unit(LPU) and an LPU-motor power interface (PI).
 6. The device as claimed inclaim 5, characterized in that the means for measuring the speed of themotor consist of a sensor (PS) delivering pulses and that the LPUcomprises means for calculating the position of the speed of the motor,a memory in which is permanently recorded the instantaneous position ofthe motor, speed and threshold presets and a preset for entry into thephase of approach to the final position, a program for comparing theposition and the measured speed with presets, and means for generating apower interface control signal.
 7. The device as claimed in claim 6,characterized in that the power interface consists of a chopped supplyand that the LPU comprises a pulse generator and pulse-width modulationmeans, the modulated pulses being applied to the chopped supply.
 8. Thedevice as claimed in claim 6, characterized in that the power interfaceconsists of a stabilized and frequency-regulated supply and that thecontrol signal generated by the LPU is a signal of variable frequency.